The application of attachable and wearable sensors has drawn extensive attention from the research community, mainly owing to the requirement for monitoring health status of humans. Ideal sensors should have high sensitivity, the capability of fast response, low costs, high reliability at the same time, and can be produced into different shapes, sizes, and geometries. In the design of a health monitoring system, the capability of deforming biosensors in response to motions such as stretching, bending, folding, and twisting is of high importance. Recently, researchers have made enormous efforts to design motion biosensors having functions of sensing breathing or joint and muscular motions. These precious research results have been widely applied to fields, for example, biomedical clothes, robotic systems, and human motion detection.
Conventional metal-based strain gauges are unable to operate at high strain levels (more than 5%), and as a consequence, they cannot efficiently fulfill requirements for biological motion detection and wearable electronic products. The previously mercury-based strain gauges, always used in biological measurement, have toxicity and limited strain performance. Based on the above, sensors that can be used for monitoring biological motion and not only can detect high strains but also have high sensitivity need to be found, so as to fulfill the development requirements of wearable electronic products.